FR2948296A1 - DEVICE FOR MIXING GAS AND DISPENSING THE MIXTURE RESULTING AT THE ENTRY OF A CATALYTIC REACTOR - Google Patents

Abstract

The device described in the present invention allows the mixing and distribution of two gases upstream of the catalytic zone of a reactor, by producing a homogeneous mixture and a speed profile as flat as possible. The device uses a plurality of internal chambers (I) enclosed in an outer chamber (II), the outer chamber communicating with each of the inner chambers by orifices pierced to the wall of said inner chambers (I) at a defined height. The outer chamber (II) is provided with a perforated plate placed at a distance H2 from the inlet tubing in said chamber (II). Application of the device to the inlet of an autothermal reactor.

Description

FIELD OF THE INVENTION The present invention is in the field of devices for producing a rapid and homogeneous mixture of gas to be reacted in a catalytic reaction zone located downstream of said device. In the context of the reactions concerned by the present invention, one of the gases is called reagent 1 and the other gas is called reagent 2. The reagent 1 is generally a vaporized hydrocarbon feedstock, optionally mixed with water vapor and reagent 2 may be pure or mixed hydrogen, air, oxygen, or any mixture of air and oxygen in any proportions. Reagent 2 may also contain a certain proportion of water vapor.

The present device can be applied to the inlet of any catalytic reactor whose diameter is between 0.05 and 10 meters, and preferably between 0.1 and 5 meters. The problem that we seek to solve the present device is to achieve a homogeneous and rapid mixture of reagents 1 and 2, and a homogeneous distribution of the gas flow resulting from said mixture over the entire inlet section of the reaction zone located downstream of the present mixing and dispensing device. Moreover, the mixture of the reagents must be as homogeneous as possible in the sense that it must have a composition of reagent 1 and reagent 2 substantially identical at any point of the inlet section in the reaction zone. Finally, the mixture must also be homogeneous from the point of view of the velocity distribution, that is, the radial velocity profile must be as flat as possible at the inlet of the catalytic reactor. EXAMINATION OF THE PRIOR ART US4865820 discloses a gas mixing device consisting of a plurality of tubes terminating in enlarged conical sections. The main gas is injected into the axis of the tubes and the secondary gas is introduced radially with respect to the tubes through orifices pierced at the wall of the tubes. The system allows a good distribution of the mixture of the main gas and the secondary gas insofar as the enlarged conical ends substantially cover the entire section of the reactor. The purpose of widening the outlet section of the tubes 30 (thus entering the reaction zone) is to reduce the speed of the gaseous mixture and to avoid the formation of vortices. In the cited patent no device is described to ensure the distribution of the secondary gas flow upstream of the introduction orifices in the tubes.

US 2002/0142199 discloses a gas mixing system including a plurality of tubes passing through a perforated plate. The first gas is injected through the tube and the second gas is injected through orifices in an annular zone between the tubes and the plate.

The gas mixture is made mainly by molecular diffusion between the two adjacent streams. As a result, the distance needed to obtain a good mixture can be relatively large. The device according to the present invention makes it possible to organize a zone called mixing zone, fed homogeneously, said zone being a zone of strong turbulence, followed in some cases by a so-called zone of distribution, which makes it possible to slow down the speed gas average and achieve entry into the catalytic zone of the reactor with a substantially flat velocity profile and a very good homogeneity of the gas mixture. SUMMARY DESCRIPTION OF THE FIGURES FIG. 1 gives a schematic view of the device according to the invention with its main dimensions in the case where the plurality of internal chambers (I) is enclosed in an external chamber (II) common to all the internal chambers. (I). FIG. 2 gives a schematic view of an internal chamber (I) according to the invention. FIGS. 3a and 3b are visualizations of the flow of the gases obtained by simulation that make it possible to assess the field of velocities and the quality of the distribution at the inlet of the catalytic zone with and without the device according to the invention.

SUMMARY DESCRIPTION OF THE INVENTION The device according to the present invention can be defined as a device for mixing and dispensing a first gas (or reactant 1) and a second gas (or reagent 2) located upstream of a catalytic zone, the two gases constituting the reagents. The device consists of a plurality of inner chambers (I) of diameter D1, an outer chamber (II) of diameter D2, each inner chamber (I) having an enlarged lower zone of exit section S2s, and in certain case of a distribution zone (W), 30 common to all the chambers (I) and being interposed between the outlet sections 2s of the internal chambers (I) and the inlet section 2r of the catalytic zone.

When it exists, the distribution zone (IV) contains elements called jet breeze, which consist of a solid plate positioned substantially horizontally, at the right of each outlet section S2s of the internal chambers (I) at a height H4 of said output section.

Each internal chamber (I) is provided with an inlet pipe El allowing the entry of the reagent 1, and the outer chamber (II) is provided with an inlet pipe E2 allowing the entry of the reagent 2 and arranged in the upper part of the outer chamber (II). The outer chamber (II) is provided with a perforated plate (1) positioned at a distance H2 with respect to the inlet pipe E2.

The device can thus be seen as an improvement of the injector concept described in US Pat. No. 4,865,820 for which the aim is to optimize the homogeneity of the supply of the mixing chamber and then the distribution of the flow resulting from said mixture. The chamber (II) communicates with each of the chambers (I) by a series of orifices (2) pierced at the wall of each internal chamber (I).

Each inner chamber (I) has an enlarged outlet end of diameter Ds and outlet section S2s. Two cases of difference are to be distinguished: a) either the sum of the exit sections 2s of the chambers (I) is equal to the section of the catalytic zone Gold, within plus or minus 10%, and then said outlet sections 20 communicate directly with the catalytic zone, b) the sum of the outlet sections Ss of the chambers (I) is strictly smaller than S2r, and then an area (IV) is formed between the outlet section of each internal chamber (I) and the inlet section S2r of the catalytic zone, zone (IV), said zone of distribution, said zone (IV) having a height H3 of between 20 and 200 mm, and preferably between 50 and 100 mm, and comprising a plurality of jet booms positioned at the right of each output section S2s at a height H4 with respect to said output sections. The enlarged zone (III) of each internal chamber (I) extends from the portion of the internal chamber (I) pierced with the orifices (2) to the outlet end S2s thereof. It has conically shaped walls at an angle (a) to the vertical. The device according to the invention therefore consists of the plurality of internal chambers (I), of the external chamber (II) common to the plurality of internal chambers (I), of the enlarged zone (III)

of each internal chamber (I) of outlet section S2s, and depending on the sum of the outlet sections 2s referred to the inlet section of the catalytic zone S2r, of the distribution zone (IV) provided with a plurality of jet bumps located at the right of each of the output sections S2s. The device according to the invention also has the following characteristics: a height H2 of between 20 and 300 mm, and preferably between 50 and 150 mm, an enlarged zone (III) on each of the internal chambers (I) having a conical shape enlarged in the direction of flow of the reagents, the angle (a) of the walls of said mixing zone relative to the vertical being between 5 ° and 45 °, and preferably between 7 ° and 25 °. a ratio of the sum of the outlet sections S2s of the internal chambers (I) on the inlet section of the catalytic zone S2r between 0.1 and 1, and preferably between 0.3 and 1 according to a variant of the device according to the invention, the jet breeks equipping the distribution zone (IV), when it exists, are positioned at a distance H4 with respect to the outlet sections of each internal chamber (I), such that H4 is equal to /(2.JPrÇ 3) within plus or minus 15%. In a preferred variant of the device according to the invention, the perforated plate (1) equipping the outer chamber (II) has a degree of opening of between 5% and 50%, and preferably between 10% and 30%. The degree of opening is defined as the ratio of the open area to the geometric section of the plate. The pitch between the orifices of the perforated plate (1) is preferably between D '/ 3 and D' / 10, denoting by D 'the difference between the pitch separating the internal chambers (I) and the diameter (D1) of said internal chambers (I). The density of the inner chambers (I) is between 10 and 500 per m 2 of the outer chamber section (II), and preferably between 20 and 100 per m 2 of the outer chamber section (II). In another particular variant of the device according to the invention, the plurality of internal chambers (I) is reduced to only one and in this case, the pitch between the orifices of the perforated plate (1) is less than D / 3, and preferably less than D / 10, D denoting the difference between the diameter D2 of the outer chamber (II) and the diameter D1 of the inner chamber (I).

The invention relates in one of its applications to the process of autothermal vapor reforming of hydrocarbon cuts, using the device according to the invention, in which the fuel gas consists of the hydrocarbon fraction and of the water vapor, and the oxidizing gas consists of air and water vapor. The hydrocarbon fraction can be any mixture of hydrocarbons of different chemical families (paraffins, olefins, aromatics) with a number of carbon atoms ranging from 1 to 20, and preferably between 1 and 10. DETAILED DESCRIPTION OF THE INVENTION INVENTION The invention consists of a device for mixing and dispensing two reactive gaseous reactants 1 and reactive 2, in order to feed a catalytic zone located downstream of said device. The device is located upstream of the catalytic zone of the reactor. , and allows to deliver in said catalytic zone a homogeneous gas mixture and having a radial distribution of the most uniform speed possible.

By radial velocity distribution is meant the profile of the velocity of the gas according to any diameter of the inlet section of the reactor. It is essential for certain types of reactions, including combustion reactions, that the gaseous mixture is as homogeneous as possible at the inlet of the catalytic zone, since any heterogeneity may result in the formation of a hot spot, or more generally of a thermal imbalance within said catalytic zone. The gases to be mixed can be distinguished into a first gas, said reagent 1, constituting the charge that may further contain water vapor, and a second gas, said reagent 2, generally containing oxygen and steam. water, possibly nitrogen and CO2, or other inert gases.

The following description is made with reference to Figures 1 and 2. The device of the present invention is composed of two chambers, a plurality of chambers (I) for the introduction of the reagent 1, called internal chambers (I), l other unique for the introduction of the reagent 2, said outer chamber (II). The plurality of substantially cylindrical internal chambers (I) is surrounded by the substantially cylindrical outer chamber (II). Each of the internal chambers (I) has an entry marked E1. The outer chamber (E2) has an inlet E2 placed in the upper part of the outer chamber (II).

The plurality of internal chambers (I) is placed in communication with the outer chamber (II) by a set of orifices (2) pierced in the walls of the internal chambers (I) at a distance (H1) located with respect to the tubing input E2 substantially equal to twice the distance (H2) separating the inlet pipe E2 from the perforated plate (1).

The reagent 2 introduced through the inlet E2 of the outer chamber (II) passes into the internal chambers (I) through the orifices (2). Each inner chamber (I) has in its lower part and up to its outlet end conical widening ending in the outlet section 2s. This enlargement is noted zone (III) in FIGS. 1 and 2.

The pitch between the orifices of the perforated plate (1) is preferably between D '/ 3 and D' / 10, denoting by D 'the difference between the pitch of the internal chambers (I) and the diameter (Dl) of the chambers internal (I). The ratio of the outlet section S2s of each internal chamber (I) to the inlet section Qr of the reaction zone is generally between 0.1 and 1, and preferably between 0.3 and 1. The invention distinguishes at this level two cases: - Either the inlet section of the reaction zone S2r is equal to the sum of the output sections S2s of each of the internal chambers (I), within plus or minus 10%, and then all of said output sections S2s open directly into the reaction zone. Either the inlet section of the reaction zone S2r is strictly greater (ie more than 10%) to the sum of the exit sections of the internal chambers (I), and then the present device provides for between the outlet sections 2s of each internal chamber (I) and the reaction zone, a distribution chamber (IV) of the same section as the reaction zone is provided, and provided with a plurality of jet breezes (3) placed at the right of each output section S2s at a distance H4 from said output sections equal to: / / (2π7) à plus or minus 15%. The outer chamber (II) is provided with a perforated plate (1) positioned at a distance H2 with respect to the inlet pipe (E2), H2 being between 20 and 300 mm, and preferably between 50 and 150 mm . The perforated plate (1) has an opening degree of between 5% and 50%, preferably between 10% and 30%.

The pitch between the orifices of the perforated plate (1) is then preferably between D '/ 3 and D' / 10, denoting by D 'the difference between the pitch separating the internal chambers (I) and the external diameter ( D1) of said internal chambers (I). When the plurality of internal chambers (I) is reduced to unity, the pitch between the orifices of the perforated plate (1) is less than D / 3, and preferably less than D / 10, denoting by D the difference between the diameter D2 of the outer chamber (II) and the diameter D1 of the inner chamber (I). Each jet jet (3) is generally constituted by a solid plate placed substantially perpendicularly to the flow direction of the gases at the outlet of each inner chamber (I).

The baffle (3) essentially has the effect of dissipating the kinetic energy of the gaseous mixture from each internal chamber (I). The present device is intended to be applied to reactors whose diameter can range from 0.1 m up to 5 meters. When the reactor diameter is less than 0.3 m, the plurality of internal chambers (I) is reduced to a single internal chamber (I). The particular case of a single internal chamber (I) is within the scope of the present invention.

EXAMPLE ACCORDING TO THE INVENTION The example consists of an autothermal reactor treating a charge consisting of C4 / C5 hydrocarbons (reactant 1) and steam and using an oxidizing gas (reagent 2) consisting of a mixture of oxygen and water vapor. Table 1 below provides the flow rates, compositions and temperature of each of the two gases. The device consists of an outer chamber (II) and an inner chamber (I) completed by a distribution chamber (IV) provided with a jet breeze (3) located opposite the outlet section 25 S2s of the internal chamber (I). The device has the following dimensions related to the diameter (D2) of the outer chamber (II): - diameter of the inner chamber (I): D2 / 2 - diameter of the outer chamber (II): D2 30 - diameter of the zone of distribution (IV): 3D2 - diameter of the outlet end of the mixing zone (III): D2 - angle a: 9 °

- distance H1: 3D2 - distance H2: 3D2 / 2 - distance H3: 2D2 - diameter of the aerator: 1.25 D2 - distance H4: D2 / 5 - perforated plate (1) of degree of opening: 30% - ratio S2s / S2r of the outlet section of the mixing zone (III) on the inlet section of the catalytic zone equal to 0.5. The speeds and the compositions of the gases are simulated by application of a mechanical software. fluids commercially called FLUENT. In the case A (according to the prior art) a device was used according to the preceding dimensions but without the perforated plate (1) and without a jet breaker. In the case B (according to the invention) is added the perforated plate (1) of degree of opening 30% and a baffle (3) positioned at a distance H4 from the exit section of the zone (III) equal at 15 D2 / 5. FIG. 3a makes it possible to compare the profile of the average speeds calculated according to the diameter of the reactor taken at the inlet of the catalytic zone, that is to say on the outlet section of the distribution chamber (IV) in case A and case B. On the abscissa the ratio r of the current radius has been increased on the radius R of the reactor.

Case A corresponds to a dissymmetry of the speed field which is particularly visible at the level of the entry into the widened zone (III) where the velocity vector has a deviation with respect to the vertical axis. Case B shows on the contrary an excellent symmetry of the velocity vectors which are well distributed over the whole of the inlet section of the enlarged zone (III) and of the distribution zone (IV). FIG. 3b makes it possible to compare the concentration fields in case A and case B. On the ordinate, the fuel concentration ratio at radius r is compared with the average concentration at the inlet of the catalytic zone as a function of the ratio of the current radius r on reactor radius R for case A (dashed line) and case B (solid line).

On the abscissa the ratio r of the current radius has been increased on the radius R of the reactor. In case A (according to the prior art), an asymmetry of the concentration field is observed which extends throughout the enlarged zone (III) and the distribution zone (IV). This illustrates the importance of achieving a field of speed as uniform as possible from the contacting of the gases at the entrance to the enlarged zone (III). In case B (according to the invention) the symmetry of the concentration field is well achieved as soon as the reagents come into contact and is maintained both in the mixing zone (III) and in the distribution zone (IV). .

Claims (1)

CLAIMS1-Device for mixing and dispensing a first gas and a second gas located upstream of a catalytic zone, the device consisting of a plurality of internal chambers (I) of diameter D1, a chamber external (II) of diameter D2, enveloping the plurality of internal chambers (I), each inner chamber (I) having an enlarged lower zone terminating in an outlet section S2s, each inner chamber (I) being provided with a tubing E1 inlet, and the outer chamber (II) being provided with an inlet pipe E2 and a perforated plate (1) positioned at a distance H2 with respect to the inlet pipe E2, the height H2 being between 20 mm and 300 mm, and preferably between 50 mm and 150 mm, the outer chamber (II) communicating with each of the internal chambers (I) by a series of orifices (2) pierced to the wall of each internal chamber (I) in an area at the distance H1 from the tub E2 entrance, H 1 being substantially equal to twice H 2, and the angle (a) of the walls of the enlarged zone (III) relative to the vertical being between 5 ° and 45 °, and preferably between 7 ° and 25 °, said device being: - either such that the sum of the exit sections 2s of the internal chambers (I) is equal to plus or minus 10% close to the inlet section S2r of the reaction zone - or such the sum of the outlet sections of the internal chambers (I) is strictly less than the inlet section of the reaction zone S2r, and then the device further comprises a distribution chamber (IV) interspersed between the exit sections Bone and the inlet section S2r of the reaction zone, said distribution chamber (IV) having a height H3 of between 20 and 200 mm, and preferably between 50 and 100 mm. 2-separation device according to claim 1, wherein when the sum of the exit sections Qs of the inner chambers (I) is strictly less than the inlet section of the reaction zone S2r, the distribution zone (IV) contains a jet jet positioned at a height H4 below the outlet section 1s of each internal chamber (I), such that H4 is between s / (2 Jrca) to plus or minus 15%. 3-separation device according to any one of claims 1 to 2, wherein the perforated plate (1) equipping the outer chamber (II) has a degree of opening between 5% and 50%, and preferably between 10 % and 30%. 4-separation device according to any one of claims 1 to 3, wherein the pitch between the orifices of the perforated plate (1) is between D '/ 3 and D' / 10, denoting by D 'the difference between the pitch separating the internal chambers (I) and the diameter (D1) of said internal chambers (I). 5-separation device according to any one of claims 1 to 4, wherein the density of the inner chamber (I) is between 10 and 500 per m2 of external chamber section (II), and preferably between 20 and 100 per m2 of external chamber section (II). 15 A separation device according to any one of claims 1 to 5, wherein the plurality of internal chambers (I) is reduced to one or two at most. 7-separating device according to claim 6, wherein the pitch between the orifices of the perforated plate (1) is less than D / 3 and preferably less than D / 10, D denoting the difference between the diameter D2 of the chamber external (II), and the diameter Dl of the inner chamber (I). 8-Process for autothermal steam reforming of a hydrocarbon fraction with a carbon number of between 1 and 20, and preferably of between 1 and 10, using the device according to one of claims 1 to 7. 9-autothermal steam reforming process of a hydrocarbon fraction, using the device according to claim 8, wherein the fuel gas consists of a mixture of hydrocarbon and water vapor, and the combustion gas consists of a mixture of air and water vapor. 10 30